Two types of model silicon (Si) nanostructure are taken into account. The first one is a 'Si nanostructure without point-group symmetry', while the second one is an amorphous Si nanostructure. We perform tight-binding electronic state calculations for these systems, and elucidate their potential applicability as light-emitting devices. Our calculations show that both model structures have high radioative recombination rates compared to those obtained from conventional model Si nanostructures, and are good candidates for Si-based light-emitting devices. (C) 2002 Elsevier Science B.V. All rights reserved.